The space should be an "espace fine" (espace is feminine in that context), meaning a smaller space (En Space) than the normal space (Em Space).

The En Space is non-breakable, but the normal non-breakable space is Em in length, and therefore improper.

Note that em (current point size) and en (½ em) spaces are both wider than the regular space character (typically ¼ em). An espace fine insécable (narrow no-break space) is even smaller, usually as small as a Unicode thin space (⅕ or ⅙ em): https://jkorpela.fi/chars/spaces.html

Word, in French mode, inserts regular no-break spaces where narrow no-break spaces would be appropriate. I find this style rather irritating, but then again, I don’t read nearly enough French to get accustomed to it.

However, I do agree strongly with the late Jan Tschichold, who recommended thin spaces before question marks, exclamation marks, colons, and semicolons for other languages, too: https://www.courses.psu.edu/art/art101_jxm22/tschichold.html...

Ah, you're right, my translation of espace fine to En was incorrect, thanks for the correction.

An intriguing problem in typography is the patterns that spaces can form between words on different lines (called rivers); in traditional typography it is checked for but I don't know of any rendering engine that would do that automatically (in a browser, or on an e-reader for example).

I believe that both TeX (Knuth-Plass Line Breaking Algorithm) and InDesign (paragraph composer – expired US Patent 6,510,441) do this, so there is at least one open-source implementation that could be used as a starting point. Unfortunately though, the awareness for good and bad typography seems to be so low that this is probably not a priority for browser and e-reader vendors. It would be wonderful to have this as part of WeasyPrint or something similar.

TeX doesn't do this automatically, but is rare to see "rivers" in TeX produced publications due to the superiority of its paragraph building algorithm.

Hmmm, that's true: https://fr.wikipedia.org/wiki/Espace_fine_ins%C3%A9cable

However, LibreOffice inserts a non-breaking space U+00A0 instead :(

So the French don't break their spaces, they cut them.

Reminds me of https://sv.wikipedia.org/wiki/Sekat%C3%B6r

On the other hand, it was the English who used to have some extra space between sentences compared to the space between words. This is still the default in LaTeX, but I believe everyone turns it off by using the \frenchspacing command in the preamble.

Also German has its own verbs for "for the insertion of inappropriate spaces before a punctuation mark." and "for the insertion of inappropriate spaces after a punctuation mark."[1] which are often used in a derogatory manner in connection with people who do it wrongly.

[1] https://en.m.wikipedia.org/wiki/Plenken

That's typical of older English typography as well.

Here in a book of classics printed in 1910:

https://archive.org/details/harvardclassics40elio/page/76/mo...

And in David Hume's Essays and Treatises on Several Subjects (1753):

https://archive.org/details/essaysandtreati00humegoog/page/n...

> The french have a different speciality: punctuation marks that consist of two parts(i.e. ? ! ; :) are preceded by a space character.

Precision: a non-breaking space (unicode U+00A0) :)

LibreOffice or other word processing software automatically replace normal spaces by non-breaking spaces in that case.

But in text editors (like vim), we must do it manually (Ctrl+Shift+ua0 on Linux), typically when writing a French text in markdown, it's a bit irritating indeed.

This is usually configurable, e.g. Compose-Space-Space inserts a no-break space if the Compose key is set up, or AltGr+Space, Ctrl-Shift+Space etc.

(KDE has a dialog for customizing this under Settings→Input Devices→Keyboard→Advanced, where there are an impressive 16 possible options. It is just options to setxkbmap underneath.)

Not only is it irritating, it looks ugly as hell.

It doesn't look ugly at all if the space is of the correct length.